1. Field of the Invention
The present invention relates to a channel sensing method, and more particularly, to a channel sensing method in a wireless multi-hop network.
2. Discussion of the Related Art
Periodic channel sensing or spectrum sensing of each node which forms a network is a frequently found scheme in an environment which uses cognitive radio or a cognitive wireless multi-hop environment, and is used to detect the state of a primary user or channel which exists in a network and to select the used channel of neighboring nodes or all nodes within the network based on the information.
The channel sensing may be divided into in-band and out-of-channel channel scanning sections, and the in-band channel scanning section is a section where each node senses the node's own channel. The channel sensing at the in-band channel scanning section detects the frequency's user by temporarily stopping communication and sensing the channel which is being used. In the out-of-band channel scanning section, channel sensing refers to a process of sensing the channel band which is not used by the current node, and because network nodes do not use the channel unlike channel sensing in the in-band scanning section, communication is not stopped.
A cognitive radio network device repeatedly performs the above explained in-band and out-of-band scanning processes at regular intervals. As such, the cognitive radio network device shares a channel which is not used by the main user of the frequency. The cognitive radio network device performs communication by using a common channel which is shared between neighboring nodes as an active channel.
For example, referring to IEEE 802.22 WRAN standard for WLAN communication in a TV white space, each node is configured to periodically sense the channel, and the scanning time is divided into an inter-frame sensing section which scans the channel during a n-frame transmission period and an intra-frame sensing section which scans the channel during a single frame time so as to minimize the sensing delay.
The channel sensing period is an element which evaluates accuracy of neighboring movement connection device information. If the sensing period time is used relatively long, the sensitivity on the search of the neighboring movement connection device is lowered. In contrast, if the sensing period is used short, the sensitivity for the channel information increases so as to quickly detect the change of the channel state such as the channel use of the main user. However, the short period time increases the transmission delay time of the network according to sensing, thereby causing the data transmission failure within the network or lowering the reliability on the network disconnection.
In particular, in a distributed network environment such as an wireless multi-hop network, all nodes participate in sensing and the nodes independently determine scanning time, etc. so as to form a network, thereby causing transmission rate decrease and transmission delay increase due to channel scanning.
As described above, the channel sensing scheme which obtains available channels by all nodes' participation in sensing in a cognitive radio environment reduces the data transmission efficiency of the entire network, and thus there is a need for minimizing the sensing delay time.